Natural gas or gases resulting from petroleum refining prior to their processing are subjected to a preliminary purification from sulphurous compounds, in particular, hydrogen sulphide.
One of the prior art processes for purification of gases from hydrogen sulphide comprises its chemical interaction with solid reactants (cf. B. S. Al'tschuler, A. A. Gavrilova "High-Temperature Purification of Gases from Sulphurous Compounds", 1969, "Nauka" Publishers, Moscow, p. 51-101). This process enables fine purification of the gas, substantially 100% recovery of hydrogen sulphide, but its implementation necessitates application of high temperatures and is accompanied by the formation of large quantities of SO.sub.2 as a result of interaction of oxygen with sulphides upon regeneration of the absorbents.
Known in the art is a process for purification of a gas from hydrogen sulphide by way of oxidation thereof on a catalyst - activated carbon (cf. Journal of Catalysis, v. 35, No. 1, 1974; M. Stejns, P. Mars "The Role of Sulfur Trapped in Micropores in the Catalytic Partial Oxidation of Hydrogen Sulfide with Oxygen, p. 11-17).
The process is effectively performed within a broad temperature range of from 20.degree. to 250.degree. C. However, at temperatures of up to 200.degree. C. the resulting sulphur is cooled on the catalyst, deactivates it so that the efficiency of purification is considerably lowered. At a temperature above 200.degree. C. sulphur is oxidized into SO.sub.2, wherefore the process selectivity is impaired.
It is known to purify gas from hydrogen sulphide with the use of zeolite catalysts (Proceedings of Moscow Mendeleev Technological Chemical Institute, issue 56, 1967; M. A. Adlivankina, N. V. Kel'tsev, N. S. Torocheshnikov, Yu. I. Schumyatsky "A Study on the Process of Partial Oxidation of Hydrogen Sulphide on Zeolities", pp. 160-164). The process is conducted at low space velocities (890 hr.sup.-1) and elevated temperatures (324.degree. C.). But even under these conditions no complete recovery of hydrogen sulphide from gases is achieved.
Known is a process for purification of gases from hydrogen sulphide on a catalyst comprising bauxite (Gazovaya Promyshlennost' /Gas Industry/, No. 8, August 1966; Yu. N. Brodsky, V. I. Gerus, S. M. Goland, Ya. I. Frenkel "Production of Sulphur at the Pokhvistnevskaya Gas Compressor Station", pp. 42-44). The maximum degree of gas purification in carrying out the process as taught by this reference does not exceed 93% even at the low space velocity of 300 hr.sup.-1 and at the temperature of 280.degree. C. To achieve a 96% degree of conversion of hydrogen sulphide, it is necessary to carry out the process in two stages with separation of water at the intermediate stage to prevent deactivation of bauxite, since an increase in the concentration of water vapours from 0.9 to 12.9% lowers the degree of the gas purification after the first step from 85% to 42% (cf. U.S. Pat. No. 3,781,445 issued Dec. 25, 1973).
The gas purification from hydrogen sulphide by this process with the use of alumina does not provide for a high selectivity of the process. Thus, at the temperature of 235.degree. C. and space velocity of 3,000 hr.sup.-1 nearly 20% of hydrogen sulphide are converted into sulphurous anhydride (Newsletters of Higher School, "petroleum and Gas", No. 2, February 1979; T. G. Alkhazov, A. A. Vartanov "On Catalytic Oxidation of Natural Gas Hydrogen Sulphide", p. 41-44).
Carrying out the process with the use of iron-oxide catalyst does not provide high process characteristics within a wide range of space rates and temperatures either. At the space velocity of 15,000 hr.sup.-1 and at the temperature of 300.degree. C. the degree of the gas purification is not more than 95%. Decreasing the space velocity contributes to a lesser selectivity of the process (cf. USSR Inventor's Certificate No. 865777, Cl. C01 B 17/04, 1981).
Also known in the art is a process for oxidation of hydrogen sulphide to elemental sulphur on a catalyst containing oxides of titanium and iron with the following content of the components, % by weight: iron oxide 0.05-0.3, titanium dioxide--the balance (cf. USSR Inventor's Certificate No. 856974, Cl. C 01 B 17/04, 1981). The maximum conversion of hydrogen sulphide into sulphur equal to 99.5% with the 100% selectivity is attained at space velocities of 2,500 to 3,000 hr.sup.-1 and temperatures within the range of from 285.degree. to 300.degree. C. This process makes it possible to purify gases with a high content of hydrogen sulphide of up to 25% by volume. A high conversion and selectivity can be attained only in carrying out the process in two stages with an obligatory intermediate trapping of sulphur and water and with separate supply of oxygen to each stage. A strictly predetermined ratio of O.sub.2 to H.sub.2 S should be maintained at each stage, this involving certain difficulties in the process control. Furthermore, as it has been already mentioned hereinbefore, a 100% conversion of hydrogen sulphide and a 99.5% selectivity of its oxidation into elemental sulphur are ensured at low space velocities of up to 3,000 hr.sup.-1 and at elevated temperatures of up to 300.degree. C.